Supercomputers and other large computer systems typically include a large number of computer cabinets arranged in banks. Each of the computer cabinets typically holds a large number of computer modules positioned in close proximity to each other for high efficiency. Each of the computer modules can include a motherboard having a printed circuit or printed wiring assembly (PWA) electrically connecting a plurality of processors, routers, and other microelectronic devices together for data and/or power transmission.
Many of the electronic devices typically found in supercomputers, such as fast processing devices, generate considerable heat during operation. This heat can damage the device and/or degrade performance if not dissipated. Consequently, supercomputers typically include both active and passive cooling systems to maintain device temperatures at acceptable levels.
Various types of passive heat-dissipation devices, such as heat sinks and heat pipe systems, have been used to cool processors and other types of electronic devices typically found in computer systems. Conventional heat sinks typically include a plurality of cooling fins extending upwardly from a planar base structure. In operation, the planar base structure is held in contact with the electronic device and heat from the device transfers into the base and then the cooling fins. Air from a cooling fan or similar device can be directed over the cooling fins to dissipate the heat.
One problem associated with conventional heat sinks is that the heat generated by the electronic device tends to be localized in discrete areas. This leads to high thermal gradients across the heat sink. As a result, most of the heat is dissipated by the cooling fins located close to the hot regions of the device. Another shortcoming of conventional heat sinks is that the air flow rate through the cooling fins is often less than the flow rate around the heat sink—an effect commonly referred to as “overpass” or “sidepass.”
Heat-dissipation devices based on heat pipe technology typically operate on a closed, two-phase cycle that utilizes the latent heat of vaporization to transfer heat. One conventional heat pipe system for cooling processing devices includes a planar base consisting of a porous wick structure. The porous wick structure forms an envelope that is evacuated and backfilled with just enough working fluid to saturate the wick structure. The pressure inside the envelope is set near the equilibrium pressure for liquid and vapor.
In operation, the base of the heat pipe system is held in contact with the electronic device, and heat from the device causes the local working fluid to evaporate at a pressure that is slightly higher than the equilibrium pressure. The high pressure vapor then flows away from the heat source to a cooler region of the base structure where the vapor condenses, giving up its latent heat of vaporization. The condensed fluid then moves back to the hot region of the base structure by capillary forces developed in the wick structure. This continuous cycle transfers large quantities of heat across the base structure with low thermal gradients. Like the heat sink described above, the heat pipe system can also include a plurality of cooling fins extending upwardly from the base structure to dissipate heat into a cooling air flow.
Another heat-pipe-based system that has been disclosed for cooling semiconductors is the heat spreading apparatus described in U.S. Pat. Nos. 6,158,502 and 6,167,948 to Thomas, both of which are incorporated herein in their entireties by reference. The heat spreading apparatus of Thomas includes a first planar body connected to a second planar body to define a void therebetween. The void includes a planar capillary path and a non-capillary region. The heat spreading apparatus dissipates heat by vaporizing a portion of working fluid in a hot region of the planar capillary path, condensing the fluid in a cool area of the non-capillary region, and moving the condensed fluid from the cool area of the non-capillary region to the hot region of the planar capillary path through capillarity.
The various heat pipe systems described above typically operate with lower thermal gradients than conventional, non-heat-pipe-based heat sinks. However, the efficiency of these systems is still limited by space constraints, air flow constraints, and/or other factors when used in large computer systems and other high density applications.